1. Field of the Invention
The present invention relates to a semiconductor device having a transistor over a substrate having an insulating surface and a method for manufacturing the semiconductor device.
2. Description of the Related Art
Integrated circuits have been developed, which use a semiconductor substrate called a silicon-on-insulator (hereinafter also referred to as an SOI) that has a thin single crystal semiconductor layer over an insulating surface, instead of a silicon wafer that is manufactured by thinly slicing an ingot of a single-crystal semiconductor. Integrated circuits each using an SOI substrate have been attracting attention as the ones in each of which parasitic capacitance between drains of the transistors and the substrate is reduced, improving performance of the semiconductor integrated circuit.
As a method for manufacturing SOI substrates, a hydrogen ion implantation separation method is known (for example, see Patent Document 1: Japanese Published Patent Application No. 2000-124092). The hydrogen ion implantation separation method is a method in which hydrogen ions are implanted into a silicon wafer to form a microbubble layer at a given depth from the surface, and a thin silicon layer (semiconductor layer) is attached and bonded to another silicon wafer with the microbubble layer used as a separation plane. In addition to the heat treatment for separation of a semiconductor layer, it is necessary to perform heat treatment in an oxidizing atmosphere to form an oxide film over the semiconductor layer, remove the oxide film thereafter, and perform heat treatment at from 1000 to 1300° C. in a reducing atmosphere to increase bonding strength.
On the other hand, a semiconductor device in which a single-crystal silicon layer is formed over an insulating substrate such as high heat resistant glass is disclosed (for example, see Patent Document 2: Japanese Published Patent Application No. H11-163363). The semiconductor device has a structure in which an entire surface of crystallized glass of which a strain point is higher than or equal to 750° C. is protected by an insulating silicon film and the single-crystal silicon layer obtained by hydrogen ion implantation separation method is firmly fixed over the insulating silicon film.
In the case of forming a transistor by using the semiconductor layer obtained by the above method as an active layer, there is an advantage that, for example, a latch-up phenomenon does not occur as compared to the case of forming a MOS transistor over a silicon wafer. Further, there is also an advantage that electrical characteristics of an obtained element are extremely excellent as compared to the case of forming a thin film transistor (TFT) by using a polycrystalline silicon layer, which is formed over an insulating substrate, as an active layer.